1. Field of the Invention
The present invention relates to a gas turbine moving blade of a gas turbine plant or a jet engine.
2. Description of the Prior Art
A gas turbine is constructed, as shown in FIGS. 5-6, so that air is compressed at a compressor 1 and fuel is fed into a combustor 2 to generate a combustion gas. The combustion gas is introduced into a turbine portion 3 to rotate a generator 4. The turbine portion 3 includes a stationary blade 5 and a moving blade 6. The moving blade 6 is an air cooled type for resisting a high temperature gas from the combustor 2.
FIG. 7 is a longitudinal cross sectional view showing one example of a prior art air cooled moving blade. FIG. 8 is a horizontal cross sectional view of the moving blade shown in FIG. 7. FIG. 9 is a perspective view of the moving blade, and FIG. 10 is a perspective view of same, as seen from another direction of FIG. 9 and partly cut out horizontally. High pressure air 7, discharged from the compressor 1, is introduced from a blade root bottom portion 8 of the air cooled blade 6. The high pressure air, after cooling a shank portion 9, a platform 10 and a blade profile portion 11, flows out of fine holes 12 provided at a blade face or out of fine holes 13 provided at a blade tip portion. Also, a pin fin portion 14 is provided at a blade trailing edge portion. Thus, such structure is capable of cooling the metal temperature of the moving blade.
In the prior art air cooled moving blade, there is a large difference in mass (thickness) between the shank portion, the platform and the blade profile portion. Nevertheless, at the time of steady operation, there occurs no large temperature difference between the platform and the blade profile portion and thus the thermal stress is also small. However, at a time of unsteady operation, such as stopping etc., the temperature of the blade profile portion goes down quickly, while the platform, due to its mass, takes longer for the temperature to fall. Thus, a large temperature difference occurs between the portions so that a very large thermal stress is created due to the temperature difference. A severe stress occurs at the connection portion between the blade trailing edge and the platform. Therefore, a construction for preventing a high thermal stress from occurring during unsteady or intermittent operation (start and stop) is necessary at the connection portion of the blade trailing edge and the platform.